Project 5: Human antibody reactivity to phosphorylcholine: modulation of PAR-dependent biological activities, induction by phosphoryl choline- bearing plaque bacteria, and relationship to periodontal destruction. The antibody response to phosphorylcholine (PC) has been extensively studied, yet its biological significance in humans is poorly understood. It is thought that the majority of human anti-PC reflects previous exposure to S. pneumoniae, but the protective nature of this response against infection with S. pneumoniae is questionable. We have found that human anti-PC levels are significantly higher in patients who have experienced periodontal attachment loss than in healthy subjects. Furthermore, our preliminary data and recent data from other groups indicate that a number of dental plaque bacteria species, including several streptococci, actinomycetes, and strains of F. nucleatum, H. aphrophilus, and A. actinomycetemcomitans bear PC-containing antigens. Our preliminary studies also show that human anti-PC reacts with the lipid mediator platelet-activating factor (PAF). In studies in which we have sought to understand the mechanisms PC profoundly inhibits IgG2 production, as does a PAF receptor antagonist. The implication of these findings, and our fundamental hypothesis, is that anti-PC antibodies may be induced in humans by oral microorganisms in patients with periodontal attachment loss and inflammation, and that these antibodies could impact on PAF- dependent biological activities. We propose to examine the effects of human anti-PC on such functions, including IgG2 production, cytokine release, and PMN transmigration. It is also of interest that S. pneumoniae accesses the circulation by utilizing its PC antigen to mimic the PAF molecule and enter and transmigrate endothelial cells. Our preliminary data indicate that oral antigen to mimic the PAF molecule and enter and transmigrate endothelial cells. Our preliminary data indicate that oral bacteria such as S. sanguis, actinomycetes, A. actinomycetemcomitans, and F. nucleatum may also utilize this pathway. This may explain the high levels of anti-PC in periodontitis patients. Furthermore, the ability to access the circulation by this pathway could be important in promoting risk for endocarditis and cardiovascular disease. We therefore propose to further study the biological significance of the human anti-PC response as well as the possibility that oral bacterial utilize PC to enter the circulation.